1. Field of the Invention
The present invention relates to a printed circuit board and a method of manufacturing the same.
2. Description of the Background Art
Cells such as fuel cells or electronic equipment such as hard disk drives employ printed circuit boards as transmission paths of electrical signals among circuit elements. A resist layer having a given pattern is formed on a conductive layer on a base insulating layer during manufacture of the printed circuit board. In this state, an exposed region of the conductive layer is subjected to etching using an etching solution, thereby forming a given conductor pattern. After that, the resist layer is removed. A cover insulating layer is formed to cover the conductor pattern. In this manner, the printed circuit board having the desired conductor pattern can be manufactured by subjecting the conductive layer to the etching (see JP 2008-258482 A, for example).
A material for the base insulating layer of the printed circuit board is optimally selected depending on uses of the printed circuit board. For example, the use of a porous polyimide film as the base insulating layer has been proposed in JP 2000-319442 A and JP 2003-201362 A. This reduces a dielectric constant of the base insulating layer.
However, the polyimide film used as the base insulating layer of JP 2000-319442 A has fine continuous pores. Therefore, a chemical solution such as an etching solution enters the continuous pores of the polyimide film to flow to a back surface of the base insulating layer during manufacture of the printed circuit board of JP 2000-319442 A. Alternatively, the chemical solution remains in the continuous pores of the polyimide film.
Meanwhile, the polyimide film used as the base insulating layer of JP 2003-201362 A does not have the continuous pores, and therefore the chemical solution will not enter the porous material during manufacture of the printed circuit board of JP 2003-201362 A. However, it is considered that the dielectric constant of the base insulating layer of JP 2003-201362 A is larger than the dielectric constant of the base insulating layer of JP 2000-319442 A.